It is highly desirable for tires to have good wet skid resistance, low rolling resistance, and good wear characteristics. It has traditionally been very difficult to improve a tire's wear characteristics without sacrificing its wet skid resistance and traction characteristics. These properties depend, to a great extent, on the dynamic viscoelastic properties of the rubbers utilized in making the tire.
In order to reduce the rolling resistance and to improve the treadwear characteristics of tires, rubbers having a high rebound have traditionally been utilized in making tire tread rubber compounds. On the other hand, in order to increase the wet skid resistance of a tire, rubbers which undergo a large energy loss have generally been utilized in the tire's tread. In order to balance these two viscoelastically inconsistent properties, mixtures of various types of synthetic and natural rubber are normally utilized in tire treads.
Snow/ice tires need to demonstrate excellent grip properties on snowy and icy roads especially at very low ambient temperatures. Simultaneously, the tread compound of snow/ice tires is required to show low hysteresis to promote lower rolling resistance. To achieve a low stiffness at low temperatures and low rolling resistance, it is preferable for the treads of snow/ice tires to use butadiene rubbers that have high (i.e. >95%) 1,4 cis butadiene content, generally referred to as cis-BR. However, an undesirable effect occurs through incorporating high levels of cis-BR in the tread with prolonged exposure to sufficiently low temperatures during service. This exposure may induce a phenomenon called “cold crystallization” leading to a significant increase in the stiffness of tread undermining the grip performance at low temperatures.